Pulmonary Function Test 

A pulmonary function test (PFT) evaluates how well your lungs work. PFTs measure the amount of air in your lungs, how well the lungs move air in and out, and possibly how medications affect the lungs. Your doctor may send you for PFTs to diagnose a lung disease, measure the severity of lung problems, as a pre-operative work-up or to see if a treatment is working for your lung disease.

A respiratory therapist will guide you through each test in a special exam room that has all the lung function measuring devices. Most of the tests are quick, easy and painless, but be sure to tell the therapist if you feel light-headed, tired or uncomfortable.

As your pulmonary function testing day approaches, you may feel the same anticipation you did back when had final exams in school. What will be on the tests? How should I prepare? Will the tests be hard?

If these familiar questions pop into your head, there's no need to worry. Use this guide for a quick study session, and you'll be ready to go.

What's on the test?


PFTs almost always include spirometry (sometimes called short or simple PFTs). Spirometry measures how much air you can inhale and exhale, and how fast you can blow the air out of your lungs. The therapist will ask you to place a clip on your nose to prevent air from leaking out. Then you will breathe through a mouthpiece connected to a computer that will measure and record your results.

Inhalation Challenge Tests

The therapist may also measure how your lungs respond to small amounts of allergens that may be causing asthma or wheezing. These are called inhalation challenge tests, or pre- and post-bronchodilator tests (these can be either short or complete PFTs). With this test, you will perform the spirometry portion of the test, receive a breathing treatment with a bronchodilator medication (most likely albuterol), and then do the spirometry portion of the testing again to measure how much your values have improved.

Pulse Oximeter

With a doctor's order, the therapist may also measure the amounts of oxygen and carbon dioxide in your blood. A pulse oximeter can measure the oxygen in your blood without using a needle.

Arterial Blood Gas

If the doctor needs more detailed information, the therapist may perform an arterial blood gas (ABG). She will draw blood from an artery, most likely from the inside of your wrist, for analysis with you sitting or lying down and resting. Sometimes, the doctor also asks for this arterial blood gas to be drawn while you exercise. This will be done with you lying down on a bed, pedaling an exercise bicycle that is at the end of the bed.

Total Lung Capacity

Another important measure is total lung capacity (or lung volume), which measures the total amount of air your lungs can hold. You will perform this test one of two ways. You will either be in a body plethysmograph, a transparent acrylic booth that is like a telephone booth, or you will do what's called a nitrogen washout. With the body plethysmograph, you will sit inside and breathe into the same tube used for the spirometry, but the door to the box will be closed for approximately 60 seconds. The alternative to this test, as mentioned before, is the nitrogen washout. You will inhale a concentration of oxygen for a short period of time (with the door to the box open) to help determine your lung capacity. The therapist will determine which of these two tests is right for you because of your specific health problems. Either way, the computer will measure your lung volumes.

Diffusion Capacity

The PFT test called diffusion capacity (DLCO) provides information about the transfer of gas between the alveoli and the pulmonary capillary blood. The NMMC lab uses the single breath or intra breath method, which involves your breathing through the same mouthpiece as with the spirometry.

The complete pulmonary function test (or complete PFT) requires you to perform the spirometry, lung volume, and DLCO.

Methacholine Challenge

The therapist may perform tests that measure how your lungs respond to outside factors such as medications, allergens or exercise. This test is called the methacholine challenge. After your initial testing, if your doctor orders, you may be asked to inhale a special medication called methacholine to see if your airways react. The test will be repeated at different doses. You will receive a breathing treatment after the test with a bronchodilator (most likely Albuterol).

Cardiopulmonary Stress Testing

For cardiopulmonary stress testing, you will undergo the baseline testing described above, and then you will be asked either to use an exercise bicycle or walk or jog on a treadmill. The purpose is to see what effect exercise has on your airflow.

These are the most common PFTs, but your doctor may request additional tests.

How can I prepare?

Tell your doctor if you have had recent chest pains or a heart attack, if you take medications for a lung problem, if you are allergic to any medications, or if you are pregnant or nursing a child. Bring a list of all the medications you are taking. You may be asked to refrain from using your inhaled bronchodilator four to six hours before the tests; check with your doctor if you have any questions about this.

Don't eat a heavy meal right before the test, and avoid caffeinated foods or drinks. Don't smoke or exercise strenuously for six hours before the test. On the day of the test, wear loose clothing that won't restrict your breathing, and wear dentures to the testing if you normally wear them.

Finally, just relax, breathe easy and do your best — these grades won't go on your permanent school records!

Contact Us

For information about Respiratory Care at NMMC, call (662) 377-4474. To learn more about Pulmonary Care, call (662) 377-4471.